Support for a machine tool portal driven by linear motors on both sides

ABSTRACT

A mounting assembly for a machine tool carriage is driven by linear motors (4) at each end guided on fixed parallel rails running parallel to one another. At each end the bridge of the carriage has bearing plates seated on the linear motor friction plates against which it is urged by spring force. As each end of the bridge has a mounting bolt extending through the bridge and bear plate and is pivotably seated in a guide aperture in the carrier. On at least one end of the bridge, the guide bolt aperture is elongated so that the bridge can pivot about the guide bolt at the other end.

BACKGROUND OF THE INVENTION

The invention is directed to a mounting assembly for a machine toolcarriage driven by linear motors on both sides of the machine tool.

A machine tool of the type which uses sliding carriages guided on railson the machine tool frame is driven on both ends by linear motors. Thesliding carriages work together to perform relative motion to oneanother as workpiece carriers as is known in German Patent 4307482 A1.Each sliding carriage is guided on a pair of parallel spaced main rails.The linear motors are mounted on both sides of the sliding carriage andturned 90° laterally to the rails. Generally, the motors are mounted ona slide on one side and with an additional guide on the other side.Compensation of stresses and torsional forces is not provided by theslide mounting.

In German Patent 24 12 769 entitled "Column Guide for the Press Plate ofa Press", it is known that a small bearing clearance can be achieved byguiding the press plate with bearing pairs on flattened surfaces on thecolumns so that the bearing pairs only are associated with two columnslying beside one another. Only a single bearing is associated with afurther column, so that, of the six degrees of freedom of the pressplate intended as a fixed body, five are guides. By this reduction ofthe guiding bearings from eight to five, the kinetic redundance indetermination is eliminated and guidance independently of stresses anddangerous torques is achieved. However, application of the principle forthe protection of linear motors running on rails from stresses ordangerous torques in a machine tool carriage as well as from accidentaldamage to the machine tool carriage appears to be only conditionallypossible.

Therefore the object of the invention is to provide a novel mounting fora machine tool carriage driven by linear motors on both sides on fixedrails to compensate for stresses and torques on the machine toolcarriage.

SUMMARY OF THE INVENTION

In accordance with the invention, this object is achieved by thefeatures named in the first claim. Advantageous embodiments of theinvention are the subject of the subclaims. The subject of the inventionis a mounting assembly for a machine tool carriage driven with linearmotors on both sides in the same direction. The linear motors are guidedon fixed rails running parallel to one another. The linear motors carryfriction contacts on which the machine carriage bridge is seated andagainst which it is pressed by its own weight and by spring force. Thebridge is movable on the friction contacts by lateral forces whichovercome the frictional force, and may be turned on the frictioncontacts. The bearing surfaces of the machine carriage bridge haveapertures which are elongated in the longitudinal direction of themachine carriage bridge. For guiding the machine carriage bridge, thebearing surface at one end of the bridge has a bolt in a guide, whilethe other bearing surface has an elongated aperture. The spring forcecan be adjusted by special adjusting screws which are seated in thefriction contact and surrounded by an open space in the bearing surfacesof the machine carriage bridge, and compression springs are disposedbetween the head of the adjusting screws and the bearing surfaces of themachine carriage bridge.

In the case of stresses in the machine carriage bridge or in the case ofdeviations of the rails from a parallel course, the lateral forcescreated in this case can be compensated by motion of the bearingsurfaces of the carriage relative to the friction contacts guided by theelongated aperture. Accidents, in particular as a result of unevenstarting of the motors, or even starting of the linear motors inopposite directions, are avoided by movement of the bearing surfaces onthe friction contacts around the bolts. The operating position of themachine carriage bridge can be reached again after an accident bycontrolling a linear motor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary end elevational view in partial section of amachine tool with a carriage assembly embodying the present invention;and

FIG. 2 is a fragmentary plan view of the assembly of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A machine tool carriage 1 is supported on a machine bed 2. The machinebed 2 bears rail pairs 3 running parallel to one another, on each ofwhich is mounted a linear motor 4 with guides 5. Each linear motor 4supports a friction plate 6, in which adjusting screws 7 for springs 8and pivotal bolts 9a and 9b are mounted. A machine carriage bridge 10with bearing plates 11 lies on the friction plates 6 and is securedthereto by the bolts 16 and adjusting screws 7. An open area or space 12is provided in the bearing plates 11 around each adjusting screw 7. Thesprings 8 are compressed between the screw head 13 of the adjustingscrew 7 and the top of the bearing plate 11. The pivotable bolt 9aextends through the bearing plate 11 and is seated in a guide 14. Thebolt 9b extends through a hole or slot 15 in the bearing plate 11 andextends in the longitudinal direction of the machine carrier bridge 10.The bolt 9b has side surfaces 16, which abut the longitudinal side wallsdefining the longitudinal hole or slot 15.

The machine carriage bridge 10 is pressed against the friction plates 6by its weight and additionally by the adjusted spring force of thesprings 8 acting on their bearing plates 11. As soon as forces caused bystresses in the machine carriage bridge 10 or by deviations of the railpairs 3 from a parallel course overcome the force of friction betweenthe friction plate 6 and the bearing plate 11, the bolt 9b slides andpivots in the longitudinal hole or slot 15. In the case of an accidentor in the case of non-uniform starting or even in the case of startingof the linear motor 4 in the opposite direction, the machine carriagebridge can be obliquely turned about the bolts 9a and 9b. Here also thebolt 9b slides in the longitudinal hole or slot 15 compensating for thechanged spacing between them. The movement of the machine carriagebridge 10 is possible by means of the open spaces 12 surrounding theadjusting screws 7. After eliminating the cause of the accident, themachine carriage bridge 10 is brought back into the operating positionby controlling only one linear motor 4, and the linear motors, thebearings therefor, and the machine carriage bridge 10 will have sufferedno damage.

Having thus described the invention, what is claimed is:
 1. In a machinetool, the combination comprising:(a) a bed with horizontally spacedportions, (b) fixed parallel rails extending along said bed portions,(c) a machine tool carriage movable along said rails and including abridge extending between said bed portions, (d) electrically drivenlinear motors at each end of said bridge for moving said carriage alongsaid rails, (e) a mounting assembly mounting each end of said bridge onone of said linear motors, said mounting assembly including:(i) afriction plate between said bridge and the linear motor, (ii) biasingmeans biasing said bridge towards said linear motor, and (iii) guidebolts mounting said bridge on said motor, said bolts extending throughand being pivotable in apertures in said bridge and said friction plate,said apertures at one end of said bridge being elongated in thelongitudinal direction of said bridge to allow pivoting of said bridgerelative to said linear motors about said bolts at the other end of saidbridge.
 2. The mounting assembly for a machine tool carriage inaccordance with claim 1 wherein said bolts in said elongated apertureshave side surfaces which abut the elongated sides of said aperture. 3.The mounting assembly for a machine tool carriage in accordance withclaim 1 wherein said biasing means comprises compression spring meansand the force is adjustable by adjusting screws adjustable independentlyof the pivotable bolts.